Out of nearly a million structures, Coppens’ 1994 solution is chosen, along with scientific superstars, such as the double helix

According to the C&E News article, Coppens' solution of the nitroprusside structure (above) "set the stage for using X-ray crystallography to examine dynamics."

BUFFALO, N.Y. – An X-ray crystal structure solved by a
University at Buffalo chemistry professor has been chosen as one of
the world’s top 10 molecular structures ever solved.

The list was compiled
by the science and technology magazine of the American Chemical
Society, Chemical & Engineering News (C&E News), to
celebrate the 100 anniversary of X-ray crystallography, the
technique that gave scientists their first peek into the atomic
world. The United Nations has designated 2014 as the International
Year of Crystallography.

In the Aug. 11 issue of C&E News, the editors wrote that
choosing 10 favorite X-ray crystal studies was tough.
“That’s no easy task: there are now nearly 1 million to
choose from. But we persevered. We zeroed in on a handful that
answered pressing chemical questions of their day.”

The editors chose the work
of Distinguished Research Professor of Chemistry Philip Coppens
from the 1990s because it ushered in a new era of X-ray
crystallographic research, allowing chemists to study short-lived,
excited-state molecules. Until that point, the technique had only
allowed scientists to study molecules when they were inactive.
Because molecules often pass through excited states just before
reacting, they were of special interest to chemists.

A few months ago, Coppens was contacted by a C&E News
editor.

“I was called for some information for an issue
highlighting a hundred years of crystallography,” says
Coppens, “but I was not told in what context. I only found
that my structure was in the top 10 when some friends in Europe,
who received the issue earlier, wrote to congratulate me.

“What did I think? Well, I knew that we were attempting
things that had not been done before and which would be important,
because the excited states we wanted to probe were structurally
unknown and very reactive precursors in chemical reactions,”
he recalls. “But I did not expect that we would be quoted on
par with the DNA double helix, transfer RNA and other structures of
such importance.”

In the early 1990s, Coppens and his UB colleagues completed what
was believed to be the first, structural study of an excited
molecule, providing scientists with a glimpse of the distortions
that a molecule undergoes in the milliseconds or nanoseconds before
it reacts chemically.

Coppens and colleagues studied sodium nitroprusside, primarily
because its presumed electronic excited state lasts for hours, far
longer than other molecules, when the crystal is cooled to very low
temperatures.

They found that in its excited state, the molecule underwent a
number of important structural changes. The 1994 achievement,
published in the Journal of the American Chemical Society, was
reported as the first X-ray crystallographic solution of a molecule
in its excited state.

But as the C&E News article recounts, scientific discovery
often takes twists and turns. Coppens and his coworkers
subsequently realized that what they were studying was not an
excited state but rather the result of a reorganization in the
molecule, produced by exposure to laser light.

The C&E News article notes that the structure Coppens solved
nevertheless “set the stage for using X-ray crystallography
to examine dynamics.” As advanced synchrotrons, which
generate very bright X-ray beams from extremely fast circulating
electrons, have come on line, it has become easier to study the
excited state.

“This story reveals something about how science
works,” says Coppens, “because we realized that we were
on the wrong track for our own project, but we had hit upon a
problem of interest by itself.”

Coppens explains that nitroprusside is part of a family of
compounds that can release nitric oxide (NO). NO has long
been of interest because of its use as a treatment for congestive
heart failure. It was, he adds, selected as Molecule of the Year by
Science in 1992 because of its action as a chemical messenger in
the body, including its ability to regulate blood pressure.

After focusing on properties of nitric oxide and related
structures, Coppens returned to the study of excited-state
molecules, and, by using very intense synchrotron sources, was able
to report the first excited state structure at atomic resolution in
2002, followed by a second one, whose excited state lasts only 11.7
microseconds.

“This work continues today,” says Coppens. “We
just submitted a report on a new study of a very short-lived
complex containing silver and copper atoms.”

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